This research project is intended to gain understanding of the interactions between the cellular elements of the nervous system and the modification of these interactions by previous activity. Experiments are proposed utilizing electrophysiological, fluorometric and morphological techniques to study the functional interdependence of neurons and glia in the optic nerve of Necturus. Following degeneration of the axons, the properties of the isolated glial cells will be studied. Glial cell turnover will be studied by autoradiography in the presence and absence of nerve axons and during axonal degeneration. Emphasis is on processes enabling glial cells to control their environment as well as the external environment of neurons. These processes include the proposed role of glia in regulating extracellular concentrations of potassium ions, amino acids and inactivating putative neurotransmitters. Further studies on the metabolic responses of glia to alterations in the ionic environment and/or membrane potential are also proposed. In addition, the electrical characteristics and the density of sodium channels of glial membranes will be studied. Electrophysiological and pharmacological techniques will be used to investigate interactions between axons and Schwann cells in squid.